Thursday, December 27, 2007

Hikers in the wilderness often place their faith in a trusty compass. But any navigator worth his salt knows that compasses can't truly be trusted: Only along certain longitudes in the Northern Hemisphere does a compass needle point due north.

In other locales, a compass needle slews either to the left or the right of true north by a certain angle, a process commonly known as declination. That's because a compass isn't attracted to the north geographic pole, the point at which Earth's rotational axis pierces the Arctic ice. Instead, the needle is attracted to the north magnetic pole, the spot where the planet's invisible magnetic field lines burst from the surface and point directly upward.

Long article on the magnetic poles and some on its relation to archaeology and history.